The Effects of Mud Rheology on Annular Hole Cleaning in Directional Wells

Summary The effects of field-measured mud rheological properties on cuttings transport in directional well drilling were studied experimentally. Water and bentonite/polymer muds were used, and angles of annulus inclination ranging from 0 to 90° from vertical. Experimental data were processed to express the cuttings transport quantitatively through annular cuttings concentration (vol%) at steady state. Three separate regions of hole inclination can be identified regarding cuttings transport: 0 to 45°, 45 to 55°, and 55 to 90°. The effect of laminar flow dominates cuttings transport in low-angle wells (0 to 45°). In high-angle wells (55 to 90°), the effect of turbulent flow predominates. In the range of intermediate inclination (45 to 55°), turbulent and laminar flow generally have similar effects. In laminar flow, higher mud yield values and yield-point/plastic-viscosity (YP/PV) ratio provide better cuttings transport. The effect of mud yield value is significant in the range of 0 to 45° hole inclination and becomes small or even negligible in the range of 55 to 90°. The effects of mud yield value and YP/PV ratio are more significant for lower annular fluid velocities. In turbulent flow, the cuttings transport was generally not affected by the mud rheological properties.